Directionally variable hearing aid

ABSTRACT

A hearing aid in which the sound reception characteristics are selectable by a user to provide non-directional or directional reception, as desired. The hearing aid employs a differential transducer having two sound receiving ports and operative to convert sound information into an electrical output and to which sound energy can be directed in one of two modes. In one mode of operation, for providing non-directional reception, sound is received from a front aperture of the hearing aid and directed to first and second input ports of the transducer, the sound being directed to the second port via an acoustic filter. In a second mode of operation, for providing directional reception, the second input port of the transducer is coupled to a rear aperture of the hearing aid and the first input port remains coupled to the front aperture. Sound energy received from the rear of the hearing aid is substantially minimized by action of the transducer without affecting energy from the front of the hearing aid. The acoustic filter in the second transducer port path during non-directional operation is used to match the frequency and phase characteristics of the non-directional mode response to the frequency and phase characteristics of the directional mode frontal response so that switching from one mode to another does not materially alter the quality of sound reception from the front direction of the hearing aid.

United States Patent 91 Johanson 1 1 Sept. 30, 1975 DIRECTIONALLY VARIABLE HEARING AID [75] Inventor: Donald L. Johanson, Wayland.

Mass.

[73] Assignee: Audivox, Inc., Newton, Mass.

[221 Filed: Aug. 8, 1974 [211 App]. No.: 495,837

Primary E.\'uminerRalph D. Blakeslee Attorney, Agent. or I-irmWeingarten, Maxham & Schurgin {57] ABSTRACT A hearing aid in which the sound reception characteristics arc selectable by a user to provide nondirectional or directional reception. as desired. The hearing aid employs a differential. transducer having two sound receiving ports and operative to convert sound information into an electrical output and to which sound energy can be directed in one of two modes. In one mode of operation, for providing nondirectional reception, sound is received from a front aperture of the hearing aid and directed to first and second input ports of the transducer, the sound being directed to the second port via an acoustic filter. In a second mode of operation, for providing directional reception, the second input port of the transducer is coupled to a rear aperture of the hearing aid and the first input port remains coupled to the front aperture. Sound energy received from the rear of the hearing aid is substantially minimized by action of the transducer without affecting energy from the front of the hearing aid. The acoustic filter in the second transducer port path during non-directional operation is used to match the frequency and phase characteristics of the non-directional mode response to the frequency and phase characteristics of the directional mode frontal response so that switching from one mode to another does not materially alter the quality of sound reception from the front direction of the hearing aid.

7 Claims, 8 Drawing Figures US. Patent Sept. 30,1975 Sheet 1 of 2 3,909,556

US. Patent Sept. 30,1975 Sheet 2 of2 3,909,556

FIG.8

DIRECTIONALLY VARIABLE HEARING AID FIELD OF THE INVENTION The invention relates to hearing aids and more particularly to a hearing aid adjustable by a user to selectively provide non-directional or directional receiving characteristics.

BACKGROUND OF THE INVENTION It is usually desirable that a hearing aid provide good non-directional response to sounds emanating from points to the front, rear and sides of a user. A particularly effective multidirectional hearing aid is described in U.S. Pat. No. 320L528, assigned to the assignee of the present invention, wherein both forward facing and rearward facing receiving apertures are provided to direct received sound information to a microphone and to provide substantially uniform gain for sounds emanating from various points about the user. In many instances however, such as in listening to lectures, conversations in a noisy environment, and the like, it would be desirable to enhance the directional characteristics of the hearing aid to accentuate the gain of sounds emanating forwardly of the user. Because of different needs in different listening situations, it is useful to provide a capability of both non-directional and direc tional characteristics in one hearing aid. A particularly effective selectable directional hearing aid is described in copending U.S. patent application Ser. No. 286,577, filed Sept. 7, I972, assigned to the assignee of the present invention.

The invention described in the aforesaid patent application attains two modes of operation by selectively occluding the rear transducer port. However, it has been found that closing the rear transducer port can cause an excessive increase in low frequency gain, resulting in a non-directional mode response characteristic stronger in the low frequencies than the directional mode frontal response. Ideally these response characteristics should be equal particularly in a high gain hearing aid wherein excessive low frequency gain can cause acoustical instability.

SUMMARY OF THE INVENTION In accordance with the present invention a selectably directional hearing aid is provided which can be operated, even at high gain levels, without undesirable instability and, which can be switched from one mode to another without materially altering the quality of the received sound from the frontal direction. Undesirable instability at high gain levels is avoided by keeping the rear transducer port open during both non-directional and directional modes of operation, and employing an acoustic filter in the path of the sound energy received at the rear port in the non-directional mode. The acoustic filter also serves to avoid undesirable material alteration of sound quality, when the hearing aid is switched from one mode to another, by selective enhancement of the low frequency response of the hearing aid in the non-directional mode, so as to approximate that of the directional mode.

The invention makes use of a differential transducer disposed inside a housing adapted to be worn by the user, the housing having a front and rear sound aperture. Disposed inside the housing are a network of sound conducting paths connecting the apertures to the transducer ports. The front aperture is always in sound communication with the first transducer port. A valve means is provided in the sound conducting paths, whereby the second port of the transducer may be made to communicate either with the rear aperture in the directional mode, or the front aperture in the nondirectional mode. I

When the valve is in the directional mode position, sound entering the front aperture is channelled to the first transducer port, while sound entering the rear aperture is channelled to the second transducer port. Sound emanating from points to the rear of a user tend to be cancelled or substantially reduced in amplitude by operation of the differential transducer, with the result that the hearing aid is most sensitive to sound emanating from points forward of the user and, thereby providing directional sound response. With the valve in the non-directional mode position, sound entering from the front aperture is channelled directly to the first transducer port along one path and, through an acoustic filter, to the second transducer port along a second path. Switching of the second transducer port to the front aperture in combination with the acoustic filter adjusts the sound energy received at the second transducer port during the non-directional mode to minimize rear port cancellation and to adjust the response characteristics of the non-directional response to approximate that of the directional front response.

The second transducer port is always in communication with a sound receiving path and the transducer is not subject to instability which can be caused under high gain conditions when the port is occluded. Thus, the hearing aid of the present invention operates well even at high gain levels and can be switched from a directional to a non-directional mode of operation without materially altering the relative quality of received sound.

The invention can be embodied in both a behind-theear type of hearing aid or in an eyeglass frame type in which the hearing aid is usually incorporated into the bow or temple of the frame.

DESCRIPTION OF THE DRAWINGS The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of a behind-the-ear type of hearing aid according to the invention;

FIG. 2 is an enlarged elevation view of the embodiment of FIG. 1;

FIG. 3 is a partly cut away enlarged elevation view of a portion of the structure of FIG. 2 with the control valve in a position opposite to that shown in FIG. 2;

FIG. 4 is a pictorial view of the invention embodied in an eyeglass type hearing aid;

FIG. 5 is a partly cut away enlarged elevation view of a portion of the structure of FIG. 4; and

FIGS. 6-8 are diagrammatic representations of an alternative embodiment of the valve assembly.

DETAILED DESCRIPTION OF THE INVENTION The invention as embodied in a behind-the-ear type of hearing aid is shown in FIG. I and includes a housing 10 adapted and configured to be worn on the ear 12 (shown in phantom) of a user and coupled by a length of tubing 14 to an earpiece l6 worn in the users ear. Included within housing 10 is a transducer for converting received sound energy into corresponding electrical energy, amplifying and processing circuitry, a battery source and volume and other controls and a receiver for transducing the amplified electrical signals into acoustical energy for conveyance via tubing 14 to the earpiece 16. Alternatively, the earpiece can include the receiver which is electrically energized via interconnecting wires from the aid circuitry.

The housing includes an upper portion 17 which extends above the ear of a user and which contains an aperture 18 which is positioned to receive sounds emanating from points forwardly of the user. A rearwardly facing aperture 20, visible in FIGS. 2 and 3, is also provided in the rear surface of upper portion 17 of housing 10 to receive sounds from points rearwardly of the user. A manually adjustable control valve 22 having a control knob 24 is provided in the upper housing portion and is operative according to the invention to alter the directional response characteristics of the hearing aid.

Referring to FIG. 2, it is seen that frontwardly facing aperture 18 communicates with valve 22 via a longitudinal channel 26 provided in the top portion of housing 10. Section 44 extends channel 26 from the valve 22 to the rear aperture 20. A differential transducer 28 is contained within housing 10 and has a first port 30 coupled to a passage 32 which is in sound communication with channel 26 at a position between aperture 1 8 and valve 22. A second port 34 of transducer 28 is coupled via a tube 36 to valve 22 via a passage 38.

An acoustic filter 50 having a cylindrical hole 51 therethrough, is disposed in channel 26 between valve 22 and the intersection of path 32 with channel 26.

The control valve 22 includes a cylinder 40 disposed within a cylindrical recess formed transversely across housing 10 and in which cylinder 40 is rotatable by action of a manual force applied to control knob 24.

An opening 41 is provided through cylinder 40, and in one position, depicted in FIG. 2, provides a sound communication path from rear aperture through the valve into passage 38, and thence via tube 36 to the second port 34 of transducer 28. With the valve 22 rotated to its second position, as depicted in FIG. 3, the passage 44 is occluded by the solid portion of cylinder 40, and a sound communication path is provided to allow aperture 18 to communicate with the first sound port of transducer 28 through channel 26 and path 32 and with the second sound port 34 of transducer 28 through channel 26, filter 50, opening 41, path 38 and tube 36.

The transducer 28 is of the differential type in which sound energy entering the second port 34 is subtracted from energy entering the first port 30, such that the transducer is responsive to the difference in received energy to provide a corresponding electrical output signal. Such transducers, also known as unidirectional microphones, are per se well known in the art, a typical example being the directional microphone manufactured by Knowles Electronics, Inc., Model BL-l687. Such a differential transducer is also described in US. Pat. No. 3,770,911.

With the control valve in the position illustrated in FIG. 2, sounds emanating from points rearwardly of a user enter the hearing aid via aperture 20 and thence via passages 44, 38 and 36 to port 34. The transducer 28 and associated valve system is operative to substan tially cancel the effects of energy emanating from the rear of aperture 20 and to provide an output signal which is essentially representative of energy received by aperture 18 and resulting from sounds from points forwardly of a user. The hearing aid in this mode of operation is therefore directional and provides enhanced reception for sounds in front of the user. In this mode the filter 50 is inoperative.

With control valve 22 in the position depicted in FIG.

3 the hearing aid is in the non-directional mode. The

port 34 of transducer 28 communicates with aperture 18 through channel 26, filter 50, path 38, opening 41 and tube 36. Port 30 of transducer 28 also communicates with aperture 18 through channel 26 and path 32. Thus for non-directional operation the rear aperture 20 is occluded and the front aperture 18 is coupled to both ports 30 and 34 of transducer 28. The rear port is always open to received sound and instability is avoided. In the non-directional mode the rear port receives sound via a filter which operates to prevent rear port cancellation in the transducer and to match phase and frequency characteristics of the non-directional response to approximate the directional front response. The hearing aid operates well even at high gain levels and switching the hearing aid from one mode to other does not materially alter the quality of sound reception emanating from the front of the user.

In the illustrated embodiment, channel 26 between front aperture 18 and valve 22 is rectangular in crosssection with a height of approximately .055 inches and a width of approximately 0.065 inches. Filter 50 fits securely in channel 26 and is approximately 0.060 inches long, with hole 51 therethrough approximately 0.016 inches in diameter. The filter 50 can be of any material and configuration providing the acoustic impedance to achieve the intended alteration of the frequency and phase characteristics of received sound. The filter can employ an opening such as shown in the illustrated embodiment, the cross-section and length of the opening determining the filtering action. The filter can also be of acoustically porous structure in which the volume and porosity determine filtering action. It will be appreciated that the acoustic filter can be formed as a separate element installed in the hearing aid or formed integrally with the housing 10.

Alternatively, the filter can be provided at other locations in the sound receiving path such as part of valve 22. As shown in FIG. 6, valve cylinder includes an opening 112 therethrough providing the intended acoustic filtering according to the invention, and a larger opening or slot 113. With the valve in a position to provide non-directional operation (FIG. 7), opening 112 communicates between passages 114 and 116 which are coupled respectively to the front hearing aid aperture and the second transducer port. Passage 118 coupled to the rear aperture is occluded. With the valve in the position providing directional operation (FIG. 8), passages 116 and 118 are interconnected via opening 113, with filter opening 112 being of no effect.

The directional receiving pattern of the hearing aid is essentially cardioid in shape, as is usual for directional microphones, and the particular pattern can be varied as desired by adjusting the distance between apertures 18 and 20 to effectively vary the pressure pattern on transducer ports 30 and 34.

The invention can also be embodied in hearing aids other than behind-the-ear types; for example, the invention can be implemented in an eyeglass frame type of aid as shown in FIG. 4. Referring to FIG. 4, there is shown a temple 55 of an eyeglass frame, the temple having a differential transducer and a network of sound conducting passages mounted therein as shown more particularly in FIG. 5. The temple further has a front aperture 56 and a rear aperture 58, each of which is disposed on the downward facing surface of temple 55. A manual valve 62 is disposed in the temple between the front and rear apertures 56 and 58 and protrudes through the top of the temple. The associated elements of the hearing aid, such as processing electronic circuitry 66 and volume control 68, are disposed in temple 55 in any convenient packaging arrangement. An earpiece 70 is provided for mounting in the ear of the user and is coupled to receiver 71 by means of a tube 72.

Referring now to FIG. 5 the internal arrangement of ports within temple 55 will be described. Forward aperture 56 communicates via channel 81 with first input port 82 of transducer 90. Passage 83 provides a sound path from channel 81 to valve 62. Passage 84 provides a sound path between valve 62 and a second input port 86 of transducer 90. Passage 85 provides a sound path between valve 62 and rear aperture 58.

The control valve 62 includes a cylinder 100 disposed within a cylindrical recess formed transversely across temple 55 and in which cylinder 100 is rotatable by action of a manual force applied to control valve stem 64. An acoustic filter 92 having a cylindrical hold 93 therethrough is disposed in passage 83 between the valve 62 and the intersection of path 83 with channel 81.

An opening 102 is provided through cylinder 100 and in one position, as depicted in FIG. 5, passage 85 is occluded by the solid portion of cylinder 100 and a sound communication path is provided to allow aperture 56 to communicate with the first sound port 82 of transducer 90 through channel 81 and with the second sound port 86 of transducer 90 through channel 81, filter 92, passages 83 and 84. This represents the nondirectional mode of operation which is as previously described for the behind-the-ear embodiment of the invention.

With valve 62 in the other position, sound entering rear aperture 58 comunicates through passages 85 and 84 with the second sound port 86, and passage 83 is occluded. This represents the directional mode of operation as previously described for the behind-the-ear embodiment of the invention.

It will be appreciated that the invention can be implemented in different ways to suit particular operation requirements. For example, the control valve can be of many different configurations to provide the intended function and the particular sound communication paths between the front and rear apertures for coupling forward and rearward sounds to the differential transducer can be selected to suit specific constructional requirements of a particular embodiment. Accordingly, it is not intended to limit the invention by what has been particularly shown and described except as indicated in the accompanying claims.

What is claimed is:

l. A hearing aid comprising:

a differential transducer having first and second sound receiving ports;

a housing having a forwardly facing sound receiving aperture and a rearwardly facing sound receiving aperture;

a first sound receiving path between said forwardly facing aperture and said first transducer port;

a second sound receiving path distinct from said first sound receiving path for selectively coupling said second receiving port to said first or second sound receiving apertures and including control valve means operative in a first position to couple sound energy received by said rearwardly facing aperture to said second sound receiving port, and in a second position to couple sound energy received by said forwardly facing aperture to said second sound receiving port;

acoustic filter means in said second sound receiving path only when said valve means is in said second position;

electronic circuitry for amplifying and processing sound information received by said transducer; and

an earpiece coupled to said circuitry and adapted to the ear of a user.

2. A hearing aid according to claim 1 wherein said first sound receiving path includes a first passage between said forwardly facing aperture and said valve means, and a second passage between said first passage and said first transducer port; and said second sound receiving path includes said first passage and a third passage between said rearwardly facing aperture and said valve means, and

a fourth passage between said valve means and said second transducer port;

said valve means being operative in its first position to provide a sound receiving path through said third and fourth passages, and operative in its second position to provide a sound receiving path through said first and fourth passages.

3. A hearing aid according to claim 2 wherein said valve means includes a rotatable member disposed at the juncture of said first, third and fourth passages and having an opening therethrough for coupling said third and fourth passages in said first position, and for coupling said first and fourth passages in said second position; and

a manually actuable control knob attached to said rotatable member and operative to rotate said member between said first and second positions. 4. A hearing aid according to claim 3 wherein said filter means is in said rotatable valve member.

5. In a hearing aid having a predetermined directional mode response and a selectably operable predetermined non-directional mode response and including:

a housing having a forwardly facing sound receiving aperture and a rearwardly facing sound receiving aperture;

a differential transducer in the housing having first and second sound receiving ports;

a network of sound conducting passages in the housing connecting the apertures to the ports; and

a valve means for selectably coupling the rear transducer port to either the front or. rear aperture;

the improvement comprising:

a sound conducting passage containing an acoustic filter for selectively varying the frequency and phase characteristics of received sound only when said rear transducer port is coupled by said valve means to said front aperture of said houswhereby the frequency and phase characteristics of sound energy emanating from the front of the wearer are not materially altered when the aid is switched from one mode to to the other. 6. A hearing aid comprising: a housing; 7 a differential transducer within said housing having first and second sound receiving ports; a channel in said housing extending between a front sound aperture and a rear sound aperture; a first sound passage coupled from said channel to said first port of the transducer; a second sound passage coupled from said channel to said second port of the transducer; valve means at the intersection of said channel and said second passage operative in a first position to couple said second port of said transducer to said rear aperture and operable in a second position to couple said second port of the transducer to said front aperture; an acoustic filter disposed in said channel between said first and second passages; means operative in response to the signal output of said transducer for providing an output signal suitable for coupling to the ear of a user. 7. A hearing aid adapted to be disposed in the temple of an eyeglass frame and comprising:

a differential transducer having first and second sound receiving ports; a first receiving aperture in the temple of said eyeglass frame forward of the ear position of a user; a second sound receiving aperture in said temple of said eyeglass frame forward of the ear position of a user and rearward of the first sound receiving aperture;

a first physically distinct sound receiving path between said forward aperture and said first transducer port;

a second physically distinct sound receiving path for selectively coupling said second receiving port to said first or second sound receiving apertures and including control valve means operative in a first position to couple sound energy received by said rearward aperture to said second sound receiving port, and in a second position to couple sound energy received by said forwardaperture to said second sound receiving port;

acoustic filter means coupled to said second receiving path only when the valve means is in said second position;

electronic circuitry for amplifying and processing sound information received by said transducer; and

an earpiece coupled to said circuitry and adapted to the ear of a user. 

1. A hearing aid comprising: a differential transducer having first and second sound receiving ports; a housing having a forwardly facing sound receiving aperture and a rearwardly facing sound receiving aperture; a first sound receiving path between said forwardly facing aperture and said first transducer port; a second sound receiving path distinct from said first sound receiving path for selectively coupling said second receiving port to said first or second sound receiving apertures and including control valve means operative in a first position to couple sound energy received by said rearwardly facing aperture to said second sound receiving port, and in a second position to couple sound energy received by said forwardly facing aperture to said second sound receiving port; acoustic filter means in said second sound receiving path only when said valve means is in said second position; electronic circuitry for amplifying and processing sound information received by said transducer; and an earpiece coupled to said circuitry and adapted to the ear of a user.
 2. A hearing aid according to claim 1 wherein said first sound receiving path includes a first passage between said forwardly facing aperture and said valve means, and a second passage between said first passage and said first transducer port; and said second sound receiving path includes said first passage and a third passage between said rearwardly faciNg aperture and said valve means, and a fourth passage between said valve means and said second transducer port; said valve means being operative in its first position to provide a sound receiving path through said third and fourth passages, and operative in its second position to provide a sound receiving path through said first and fourth passages.
 3. A hearing aid according to claim 2 wherein said valve means includes a rotatable member disposed at the juncture of said first, third and fourth passages and having an opening therethrough for coupling said third and fourth passages in said first position, and for coupling said first and fourth passages in said second position; and a manually actuable control knob attached to said rotatable member and operative to rotate said member between said first and second positions.
 4. A hearing aid according to claim 3 wherein said filter means is in said rotatable valve member.
 5. In a hearing aid having a predetermined directional mode response and a selectably operable predetermined non-directional mode response and including: a housing having a forwardly facing sound receiving aperture and a rearwardly facing sound receiving aperture; a differential transducer in the housing having first and second sound receiving ports; a network of sound conducting passages in the housing connecting the apertures to the ports; and a valve means for selectably coupling the rear transducer port to either the front or rear aperture; the improvement comprising: a sound conducting passage containing an acoustic filter for selectively varying the frequency and phase characteristics of received sound only when said rear transducer port is coupled by said valve means to said front aperture of said housing; whereby the frequency and phase characteristics of sound energy emanating from the front of the wearer are not materially altered when the aid is switched from one mode to to the other.
 6. A hearing aid comprising: a housing; a differential transducer within said housing having first and second sound receiving ports; a channel in said housing extending between a front sound aperture and a rear sound aperture; a first sound passage coupled from said channel to said first port of the transducer; a second sound passage coupled from said channel to said second port of the transducer; valve means at the intersection of said channel and said second passage operative in a first position to couple said second port of said transducer to said rear aperture and operable in a second position to couple said second port of the transducer to said front aperture; an acoustic filter disposed in said channel between said first and second passages; means operative in response to the signal output of said transducer for providing an output signal suitable for coupling to the ear of a user.
 7. A hearing aid adapted to be disposed in the temple of an eyeglass frame and comprising: a differential transducer having first and second sound receiving ports; a first receiving aperture in the temple of said eyeglass frame forward of the ear position of a user; a second sound receiving aperture in said temple of said eyeglass frame forward of the ear position of a user and rearward of the first sound receiving aperture; a first physically distinct sound receiving path between said forward aperture and said first transducer port; a second physically distinct sound receiving path for selectively coupling said second receiving port to said first or second sound receiving apertures and including control valve means operative in a first position to couple sound energy received by said rearward aperture to said second sound receiving port, and in a second position to couple sound energy received by said forward aperture to said second sound receiving port; acoustic filter means coupled to said second receiving path only when the valve means is in saId second position; electronic circuitry for amplifying and processing sound information received by said transducer; and an earpiece coupled to said circuitry and adapted to the ear of a user. 